Process for bonding platinum onto a base metal

ABSTRACT

THERE IS DISCLOSED A PROCESS OF METALLURGICALLY BONDING A PLATINUM COATING TO A BASE METAL BY APPLYING TO THE BASE METAL AN EASILY REDUCED METAL WHICH WILL NOT OXIDIZE AND THEREAFTER APPLYING MOLTEN PLATINUM IN DROPLET FORM ONTO THE REDUCED METAL. THE CONTEMPLATED BASE METALS INCLUDE IRON OR NICKEL BASE ALLOYS SUCH AS INCONEL, NICHROME, AND THE LIKE. THE CONTEMPLATED REDUCED METAL IS GOLD, SILVER, OR COPPER. THE APPLICATION OF THE MOLTEN PLATINUM IN DROPLET FORM MAY BE BY A FLAME-SPRAY OR PLASMA-JET SPRAY TECHNIQUE.

Dec. 14, 1971 R. s. RICHARDS 3,627,56!

PROCESS FOR BONDING PLATINUM ONTO A BASE METAL Original Filed July 16,1965 "YMKQ/ United States Patent @thee 3,627,561 PROCESS FOR BONDINGPLATINUM ONTO A BASE METAL Raymond S. Richards, Toledo, Ohio, assignorto Owens-Illinois, Inc.

Original application July 16, 1965, Ser. No. 472,417, now Patent No.3,432,278, dated Mar. 11, 1969. Divided and this application Oct. 16,1968, Ser. No. 767,946

Int. Cl. B44d 1/08, 1/14, 1/16; C23c 7/00 U.S. Cl. 117--71 M 9 ClaimsABSTRACT OF THE DISCLOSURE There is disclosed a process ofmetallurgically bonding a platinum coating to a base metal by applyingto the base metal an easily reduced metal which will not oxidize andthereafter applying molten platinum in droplet form onto the reducedmetal. The contemplated base metals include iron or nickel base alloyssuch as lnconel, Nichrome, and the like. The contemplated reduced metalis gold, silver, or copper. The application of the molten platinum indroplet form may be by a llame-spray or plasma-jet spray technique.

RELATED CASES This is a division of copending U.S. patent applicationSer. No. 472,417, filed July 16,1965, now Pat. No. 3,432,- 278.

THE INVENTION This invention relates generally to the art of coatingmetal articles and in particular is concerned with a process formetallurgically bonding a platinum coating to a base metal.

In the chemical industry many corrosive atmospheres are present Withinwhich metal parts must be located. One metal which has exceptionallygood corrosion and/ or heat resistance is platinum. However, platinum isquite expensive and, therefore, it has been desirable to use as littleplatinum as is necessary to provide suicient protection to metal partswhich may be subjected to high temperatures and/or corrosiveatmospheres. Many iron or nickel base alloys exhibit sufficient thermalresistance so as to be capable of use at fairly high temperatures;however, in a corrosive atmosphere these metals oxidize and corrodequickly.

It has been the practice in the past to mechanically clad such basemetals with platinum sheeting. However, one serious drawback is that thethermal expansion characteristics of platinum and the base metals aresuch that there is a tendency for the platinum to buckle and warp undertemperatures in the 2000 F. and above range.

In recent times it has been the practice to flame-spray metals withcoatings of other types of metals. However, in these situations,particularly when an attempt is made to flame-spray platinum overlnconel or other iron or nickel base alloys, the ame used in sprayingthe metal will oxidize the base metal, thus producing a poor bondbetween the platinum and the base metal.

With the foregoing in mind, this invention comprises a process formetallurgically bonding platinum to base metals.

More particularly, this invention relates to a process formetallurgically bonding platinum to a base metal by utilizing an easilyreduced metal as an intermediate platedon layer.

The invention and the advantages thereof will be apparent from thefollowing description taken in conjunction with the annexed sheet ofdrawings, wherein:

FIG. 1 is a perspective view of a metal pipe having platinum appliedthereto by the improved process; and,

3,627,561 Patented Dec. 14, 1971 FIG. 2 is a block diagram illustratingthe successive steps of the improved process.

In accordance with this invention, it has been discovered that moltenplatinum can be metallurgically bonded to base metals such as iron ornickel base alloys such as a chrome-nickel steel sold under the tradename lnconel, by International Nickel Co. Nichrome and the like withoutthe production of pin holes if the base metal is first plated with a.thin, eg., .00025 inch, layer of gold or other noble or easily reducedmetal which will not oxidize at elevated temperatures, eg., at thetemperature of the molten platinum; that is, a noble metal which can bereduced and which will not oxidize during the fiamespraying of platinumthereof. After the gold or other easily reduced metal is plated on thebase metal, a flamespray or plasma-jet spray technique may be utilizedto apply the platinum in molten droplet form to the gold to a thicknessof at least about .007 inch, e.g., about .007 to about .015 inch.Whether the platinum is applied by flame-spray or plasma-jet spraytechnique is immaterial so long as there is a deposition of moltenplatinum in droplet form onto the (gold) plated base metal.

After the spray cladding, it is desirable to stress relieve and sinterthe composite structure, for example by heating to 1800 F. for two hoursfor an lnconel-goldplatinum combination. In this particular arrangementthe gold serves two purposes: (1) it provides a non-oxidized surface forthe platinum; and (2) it also serves as a brazing metal in that theplatinum dilfuses into the gold and the gold diffuses into the Inconel.Thus a metallurgical bond is established between the lnconel and theplatinum. The surface of the base metal may be roughened prior to thegold plating so as to avoid any possibility of the applied platinumseparating from the base metal during subsequent sintering. Furthermore,it has been found desirable and is preferred that the plated base metalarticle be preheated to a temperature of approximately 1200 F. and thatthe applying of the molten droplets of platinum be carried out while theplated article is hot. By this technique, the impingement and impact ofthe platinum droplets, as such strike the intermediate layer of easilyreduced metal, will assume a more flattened contour since there is asomewhat less temperature difference between the molten platinumparticles and the article to be clad. In this manner a more tenaciousand better metallurgical bond will be provided, and the formation of pinholes or random spots where the platinum, even if sprayed with severallayers, might provide an intrusion or passage through the platinumthrough the gold, is prevented.

As can be seen when referring to FIG. 1 of the drawing, the base metal10, such as lnconel, is plated with a layer of pure gold 11 and thenflame-sprayed or plasmajet sprayed with platinum to form the coating orcladding 12.

While gold has been disclosed as the preferred metal which is plated tothe clean iron or nickel base alloy, it is also possible to use copperin place of gold. However, when copper is used as the metal plated tothe iron or nickel base alloy, it is necessary to use a reducing gasshield over the plated article prior to the spraying of platinum thereonin order to ensure that the copper does not have an oxide layer orsurface when the platinum is applied thereto. Copper does exhibit theproperty that when it is being dame-sprayed, for example in a platinumflamespraying system, it tends to lose its oxide coating and appear as abright metal under the extreme heats involved in the flame-spraying.Thus, there is the tendency of the copper to clean itself of oxideduring the llame-spraying of platinum thereon.

A third plating material which may be used in accordance with theinvention is silver. Silver may be plated over the Inconel for example,in a relatively thin layer; however, it would be necessary to heat thesilver-plated article to a temperature sufficient to decompose all thesilver oxide on the surface of the silver, for example at 1200 F. Thisheating will effectively clean the silver and permit the llame-sprayingof platinum thereon, with the result that the platinum would adhere andform a metallurgical bond with the silver and the silver in turn wouldmetallurgically bond with the Inconel to produce a metallurgi-callybonded article when sintered.

As previously described, the base metal may be roughened prior to theplating of the gold, copper or silver. However, this roughening may notbe necessary, particularly in the situation Where the plating is tooccur on the outside surface, for example of a piece of pipe, since thesprayed platinum will shrink tightly around the base metal pipe. Inthose situations where the platinum is to be put on the inside of anarticle such as a pipe, either roughening, preheating or both would berequired in order to keep the sprayed platinum from pulling loose.

In all instances the step of heating to stress relieve and sinter thecomposite article is desirable in order to ensure the production of agood metallurgical bond of the platinum to the substrate.

Having described the best mode of carrying out the invention, the scopeof the invention should not be limited except as required by the scopeof the appended claims.

I claim:

1. A process for metallurgically bonding platinum to a base metal ofiron, nickel, or alloys thereof which comprises plating the base metalwith a layer of easily reduced metal selected from copper, silver, orgold and then depositing platinum in molten droplet form by llame-sprayor plasma-jet-spray into the plated base metal whereby the platinum ismetallurgically bonded thereto, said metallurgically bonded platinumhaving a thickness of at least .007 inch` 2. The process of claim 1wherein the base metal is selected from iron or iron base alloys.

3. The process of claim 1 wherein the base metal is selected from nickelor nickel base alloys.

4. The process of claim 1 wherein the easily reduced metal is copperwhich is maintained oxide free and wherein the platinum is applied in areducing gas atmosphere.

5. The process of claim 1 wherein the easily reduced metal is silver andwherein the composite structure of silver and base metal is heated toand maintained at a temperature of about 1200 F. so as to free thesilver surface thereof from oxides before the molten platinum is appliedthereto.

6. The process of claim 1 wherein the platinum is applied to a thicknessof about .007 to about .015 inch.

7. The process of claim 6 wherein the base metal is a chrome-nickelsteel.

8. The process of claim 1 wherein the composite structure of platinum,reduced metal, and base metal is heated to an elevated temperature for aperiod of time suicient to stress relieve and sinter the structure.

9. The process of claim 8 wherein the base metal is a chrome-nickelsteel, the reduced metal is gold, and the structure is heated atapproximately 1800 F. for about two hours.

References Cited UNITED STATES PATENTS 1,043,578 1l/l912 Eldred 29--1991,140,136 5/1915 Eldred 29--199 1,197,615 9/1916 Eldred 29-199 2,897,584S/l959 Schumpelt 29'-199 3,137,766 6/1964 Teague 29-199 X ALFRED L.LEAVI'IT, Primary Examiner C. K. WEIFFENBACH, Assistant Examiner U.S.Cl. XR.

29--196, 196.3, 199; ll7-93.1PF, 105, 105.1, 105.2

